A nozzle stopper system and a slide valve (sliding nozzle) system are well known as discharge regulating mechanisms of molten metal in the case of pouring a molten metal from a molten metal vessel.
It is also known that said conventional systems have the undermentioned drawbacks.
1. Nozzle stopper system
1) Since a nozzle stopper 1 approximately same in length as the molten metal vessel is required the refractory costs high.
2) As will be seen from FIG. 15 (showing a relationship of the stroke and the opening area between the slide valve and the nozzle stopper), the discharge rate greatly varies depending on a slight movement of a nozzle stopper 1 so that this system is inferior in discharge regulation.
3) Since the nozzle stopper 1 is immersed in the molten metal there occur troubles such that the nozzle stopper is broken due to melting-down or heat spalling to allow the discharge regulation to be unable.
2. Slide valve system
1) In the case of ladle, it took a time from some ten minutes to several hours during the period from receiving a molten metal in a ladle to pouring (hereinafter called casting) the molten metal because of component control, temperature control, etc. of the molten metal.
This necessitated it to fill the interior of a nozzle 2 with a filler such as sand to prevent molten metal from solidification within the nozzle thereby lowering the working efficiency. The filler is of the idea that in case the slide valve is opened the filler first flows out and then the molten metal flows out so that the nozzle naturally opens. However, the molten metal permeates into the filler thereby to be solidified there and the nozzle sometimes does not naturally open. This necessitates the nozzle 2 to be forcedly open by an oxygen lance thus compelling the operator to a dangerous work.
2) In the case of tundish, it is unallowed to use a filler or the like in the light of quality of molten metal, and it is necessary to apply refractory, steel pipe or the like to the upper outer periphery of the nozzle so that the nozzle may open after the molten metal has accumulated in a predetermined amount. This causes unfavorable workability and high cost.
3) Again in the case of tundish, there is a method of preventing the molten metal within the nozzle from solidification by injecting an inert gas from a fixed plate 3 or a slide plate 4 as shown in FIG. 16 instead of using refractory or steel pipe. However, in such a case the mechanism of introducing the inert gas becomes complicate and it costs high.
Further, even in the method (c) above, 100% success would not be expected and the molten metal within the nozzle sometimes solidifies thereby disabling the casting from starting.
Furthermore, even when an immersion nozzle in replaced while casting the nozzle is closed, and therefore the inconvenience same as above occurs.
4) The nozzle is occasionally opened fully while casting due to an erroneous operation or any necessity. However, since the molten metal solidifies within the nozzle if the nozzle is retained fully open for a long period of time, a forced opening of the nozzle becomes necessary.
5) Since this system has a number of connecting portions and there is a great risk of inhating air from the exterior of the refractory, it is greatly possible that the quality of the product is reversely affected.
Moreover, a rotary valve as shown in FIG. 17 is a new modern technique. This system is characterized in that it consists of a rotor 20, a dome nozzle 21 and a drive mechanism 20a, the dome nozzle 21 is fixed to a tundish 23 and the rotor 20 is turned to permit the discharge flow of the molten metal to be regulated. However, even this system has the undermentioned demerits.
1) Since the rotor 20 is immersed in the molten metal a trouble occurs such that the rotor is broken due to melting-down or heat spalling, and the discharge regulation becomes disabled occasionally.
2) Since the rotor 20 is longer than the height of tundish 23 the system is costly.
3) In the initial state of casting, a nozzle 22 is fully opened, the molten metal is poured into the tundish 23, the nozzle 22 is opened after the molten metal has been accumulated in a predetermined amount, and then the casting working is started. However, the nozzle 22 itself cannot be prepared so great under the following reasons, so that the molten metal solidifies because of the lowered temperature of the molten metal within the nozzle 22 thereby disabling sometimes the casting from starting.
That is, to make the nozzle 22 large-sized results in that the rotor 20, the dome nozzle 21 and other related members need to be large-sized whereby it leads to an increase of cost and problematical workability. Thus, to make the nozzle 22 large-sized is naturally limited to a certain extent.
On the other hand, in an emergency such as incorrect operation during the casting working or overflow of the molten metal within the mold the nozzle 22 may occasionally be opened fully, but in such a case the molten metal within the nozzle 22 solidifies as described above when it becomes impossible to restart the casting.
4) Since the rotor 20 is great and heavy its handling and setting work is inconvenient.